The present invention relates in general to an air conditioning installation for a motor vehicle, and in particular to an air conditioning installation for a motor vehicle with a cold reservoir, which can be charged with cold produced in an evaporator of a primary circuit.
An air conditioning installation with the characteristics of the preamble to claim 1 for a refrigerated goods vehicle is known from "Ki Klima-Kalte-Heizung", June/1988 page 286, paragraph 3.1. The air conditioning installation includes a cold reservoir, which is produced in the form of a water tank which can equally well serve as an ice container. The cold reservoir can be charged from an evaporator of a primary circuit, the primary circuit, in the known way, forming a cooling circuit, which contains a compressor unit, a condenser and an expansion unit, in addition to the evaporator. The air conditioning installation of the generic type described here further includes a heat exchanger, which can deliver cold stored in the cold reservoir to the interior of the motor vehicle via a secondary circuit. With the air conditioning installation described here, this heat exchanger is charged with ice water from the reservoir by a circulating pump via a water circuit. The known air conditioning installation exhibits relatively sluggish response characteristics, because the entire volume of the water held in the reservoir has to be cooled, before the desired cooling can be made available via the heat exchanger. Moreover, the growth of the ice in the reservoir has to be controlled, the ice production and melting having to be kept in balance while the vehicle is in operation.
In view of the above-described drawbacks, so-called installations with a secondary evaporator have been developed. Such an air conditioning installation is likewise known from "Ki Klima-Kalte-Heizung", June/1988 page 286, paragraph 3.3. In this implementation, two cooling circuits are generally provided. The primary cooling circuit, in the usual way, includes a compressor unit, a condenser, an expansion unit and a primary evaporator, the primary evaporator serving, while the vehicle is in operation, to make the desired cooling power available for the refrigerated goods vehicle. The second cooling circuit is formed from the compressor unit and the condenser of the primary circuit, supplemented by a further expansion unit and a secondary evaporator, which is contained in an ice/water cold reservoir. The two cooling circuits are laid out in such a way that the primary evaporator and the secondary evaporator are connected in parallel. The known air conditioning installation thus allows the following modes of operation, while the vehicle is operating: pure air cooling while the vehicle is operating, via the primary evaporator; cooling by means of the primary and secondary evaporator while the vehicle is operating (charging of the ice tank); charging of the ice tank while the vehicle is operating without cooling by means of the primary evaporator. With the internal-combustion engine turned off, the ice tank can be discharged via the primary evaporator when standing still by circulating the cooling fluid by means of an electric pump, in order to make cold available to the primary evaporator.
Such installations with a secondary evaporator are therefore relatively complex in construction, so that their application to refrigerated goods vehicles is restricted, in particular by the high space demands, brought about among other things by the parallel connection of primary evaporator and secondary evaporator provided in the cold reservoir. Furthermore, it is not possible with the solutions known hitherto to remove cold from the cold reservoir while the vehicle is operating, which would be desirable, for example at low engine speeds. Consequently, prior solutions provide only an interim solution. Hence, there is a need for an improved air conditioning installation, which, like the known installations with a secondary evaporator, permits full use of the storage medium, since not required for circulation, and which is nevertheless structurally simple in implementation and can therefore be integrated with low space requirements even into a private car.